<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
 <head>
  <title>CSS Reference File</title>
  <style type="text/css">
     .container {
          position: absolute;
          border: 1px solid green;
          height: 200px;
          width: 100px;
          background-color:green;
          margin-top: 150px;

      }

      .hidden {
          position: absolute;
          border: 2px solid red;
          height: 200px;
          width: 100px;
          background-color:red;
          margin-top: 150px;
      }
  </style>
  
 </head>
 <body>
  <p>You should see only 1 green box.</p>
  <div class="container">
  </div>
</body>
</html>